Question

A Petri dish contains 100 bacteria cells. The number of cells increases 5% every minute. How long will it take for the number of cells in the dish to reach 2000? Use logarithms to solve.

Answer 1

Using logarithm, the following equation will apply:
Y = P * [1 + z]^x
Where Y = 2000
P = 100
z = 5% = 0.05
x is the quantity we are calculating for
The equation becomes
2000 = 100 * [1+ 0.05]^x
Dividing both side by 100, we have 
20 = 10 * [ 1 + 0.05]^x
Taking the log of both sides, we have
Log 20 = Log [1 + 0.05]^x
log 20 = x * log 1.05
x = log 20/ log 1.05 = 61.40
Thus, it will takes 61.40 minutes for the number of cells in the petri dish to reach 2000.